Arthroscopic Ultrasound Technique for Simultaneous Quantitative Assessment of Articular Cartilage and Subchondral Bone: An In Vitro and In Vivo Feasibility Study

Traditional arthroscopic examination is subjective and poorly reproducible. Recently, we introduced an arthroscopic ultrasound method for quantitative diagnostics of cartilage lesions. Here we describe our investigation of the feasibility of ultrasound arthroscopy for simultaneous measurements of articular cartilage and subchondral bone. Human osteochondral samples (n = 13) were imaged using a clinical 9-MHz ultrasound system. Ultrasound reflection coefficients (R, IRC), the ultrasound roughness index (URI) and the apparent integrated backscattering coefficient (AIB) were determined for both tissues. Mechanical testing, histologic analyses and micro-scale computed tomography imaging were the reference methods. Ultrasound arthroscopies were conducted on two patients. The ultrasound reflection coefficient correlated with the Mankin score and Young's modulus of cartilage (|r| > 0.56, p < 0.05). Ultrasound parameters (R, IRC, AIB) for subchondral bone correlated with the bone surface/volume ratio (|r| > 0.70, p < 0.05) and trabecular thickness (|r| > 0.59, p < 0.05). Furthermore, R and subchondral bone mineral density were significantly correlated (|r| > 0.65, p < 0.05). Arthroscopic ultrasound examination provided diagnostically valuable information on cartilage and subchondral bone in vivo.     

Mitigation of Articular Cartilage Degeneration and Subchondral Bone Sclerosis in Osteoarthritis Progression Using Low-Intensity Ultrasound Stimulation

The purpose of this study was to evaluate the effect of low-intensity ultrasound on articular cartilage and subchondral bone alterations in joints under normal and functional disuse conditions during osteoarthritis (OA) progression. Total of thirty 5-mo-old female Sprague–Dawley rats were randomly assigned to six groups (n?=?5/group): age-matched group, OA group, OA?+?ultrasound (US) group, hindlimb suspension (HLS) group, HLS?+?OA group and HLS?+?OA?+?US group. The surgical anterior cruciate ligament was used to induce OA in the right knee joints. After 2 wk of OA induction, low-intensity ultrasound generated with a 3-MHz transducer with 20% pulse duty cycle and 30 mW/cm² acoustic intensity was delivered to the right knee joints for 20 min a day, 5 d a week for a total of 6 wk. Then, the right tibias were harvested for micro-computed tomography, histologic and mechanical analysis. Micro-computed tomography results indicated that the thickness and sulfated glycosaminoglycan content of cartilage decreased, but the thickness of the subchondral cortical bone plate and the formation of subchondral trabecular bone increased in the OA group under the normal joint use condition. Furthermore, histologic results revealed that chondrocyte density and arrangement in cartilage corrupted and the underlying subchondral bone increased during OA progression. These changes were accompanied by reductions in mechanical parameters in OA cartilage. However, fewer OA symptoms were observed in the HLS?+?OA group under the joint disuse condition. The cartilage degeneration and subchondral bone sclerosis were alleviated in the US treatment group, especially under normal joint use condition. In conclusion, low-intensity ultrasound could improve cartilage degeneration and subchondral sclerosis during OA progression. Also, it could provide a promising strategy for future clinical treatment for OA patients.     

超声诊断膝关节软骨退行性变的影响因素分析

目的 分析超声诊断膝关节软骨退行性变(退变)的一些影响因素.方法 选择行膝关节镜手术患者36例37个膝关节及关节置换术患者4例4个膝关节,共41个膝关节.术前1周行超声检查,超声诊断结果与关节镜或大体标本肉眼所见结果对比.对超声误诊、漏诊病例进行回顾性分析.结果 本组234处病灶,超声诊断真阳性病灶87处,假阳性病灶8处,假阴性病灶47处,真阴性病灶92处,诊断敏感性、特异性、准确性分别为64.9%、92.0%、76.5%.超声对软骨退变的分期与关节镜分期相关(r=0.703,P<0.01),但有59处病灶(59/234,25.2%)两者分期不符.影响超声诊断准确性的因素主要包括(1)病变部位,(2)病变程度,(3)临床治疗过程,(4)一些与超声成像原理有关的一般性影响因素.结论 超声检测膝关节软骨退变操作较复杂,影响因素也多.正确认识这些因素,有助于更好地理解声像图,避免漏诊误诊.     

Ultrasound Parameters for Human Osteoarthritic Subchondral Bone ex Vivo: Comparison with Micro-Computed Tomography Parameters

The aim of this study was to identify ultrasound parameters reflecting subchondral porosity (P_o), subchondral plate thickness (T_pl) and bone volume fraction at the trabecular bone region (BV/TV_Tb). Sixteen osteoarthritic human lateral femoral condyles were evaluated ex vivo using a 15-MHz pulsed-echo ultrasound 3-D scanning system. The cartilage–subchondral bone (C-B) surface region (layer 1) and inner subchondral bone region (layer 2) were analyzed; we newly introduced entropy (ENT) and correlation (COR) of ultrasound texture parameters of the parallel (x) or perpendicular (z) direction to the C-B interface for this analysis. P_o, T_pl and BV/TV_Tb were evaluated as reference measurements using micro-computed tomography. ENT_L1x (ENT of layer 1, x-direction) and ENT_L1z were significantly correlated with P_o (both r values?=?0.58), COR_L2x with T_pl (r?=?–0.73) and COR_L2z with BV/TV_Tb (r?=?–0.66). These are efficient indicators of the characteristics of osteoarthritis-related subchondral bone; the other texture parameters were not significant.     

膝关节滑膜病变的高频超声与关节镜对照研究

目的通过与关节镜结果检查对照,评价高频超声对膝关节滑膜病变的诊断价值.方法 68例临床病例,应用高频超声前瞻性观察 72个膝关节滑膜情况,并与关节镜检查结果对照,找出膝关节滑膜疾病的图像特征;并采用双盲法对高频彩超的诊断能力进行评价.结果高频超声诊断膝关节滑膜病变的敏感性为 93.3%、特异性为 90.9%,准确性为 91.7%,阳性预测值为 98.2%及阴性预测值为 71.4%.结论高频超声在术前常规筛选滑膜疾病方面是一种很有价值的影像学方法.     

High-Frequency Ultrasound Imaging of Tidemark In Vitro in Advanced Knee Osteoarthritis

High-frequency ultrasound imaging has been widely adopted for assessment of the degenerative changes of articular cartilage in osteoarthritis (OA). Yet, there are few reports on investigating its capability to evaluate subchondral bone. Here, we employed high-frequency ultrasound imaging (25?MHz) to examine in vitro the tidemark in cylindrical osteochondral disks (n?=?33) harvested from advanced OA knees of humans. We found good correspondence in morphology observed by ultrasound imaging and micro-computed tomography. Ultrasound roughness index (URI) of tidemark was derived from the raw radiofrequency signals to compare with bone quality factors, including bone volume fraction (BV/TV) and bone mineral density (BMD) measured by micro-computed tomography, using the Spearman correlation (ρ). URI of the tidemark was negatively associated with the subchondral plate BV/TV (ρ?=??0.73, p?<0.001), BMD (ρ?=??0.40, p?=?0.020), as well as the underneath trabecular bone BV/TV (ρ?=??0.39, p?=?0.025) and BMD (ρ?=??0.43, p?=?0.012). In conclusion, this preliminary study demonstrated that morphology measured by high-frequency ultrasound imaging could reflect the quality of the subchondral bone. High-frequency ultrasound is a promising imaging tool to evaluate the changes of the subchondral bone in addition to those of the overlying cartilage in OA.     

Ultrasound Biomicroscopy Imaging for Monitoring Progressive Trypsin Digestion and Inhibition in Articular Cartilage

This study reports an ultrasound biomicroscopy (UBM) imaging approach to monitor the progressive trypsin-induced depletion of proteoglycan (PG) and its inhibition in articular cartilage. Three fresh, normal bovine patellae were obtained and four full-thickness cartilage-bone specimens were prepared from the lower medial side of each patella. One sample was used as a control and the other three were divided into three groups: Groups A, B and C (n = 3 for each group). After a 40 min 0.25% trypsin digestion, samples from group A were continuously digested in trypsin solution, while those in groups B and C were immersed in physiologic saline and fetal bovine serum (FBS), respectively, for another 280 min. The trypsin penetration front was observed by UBM and M-mode images were acquired using 50 MHz focused ultrasound and custom-developed software. The results show that the 40 min trypsin digestion degraded nearly the whole surface layer of the cartilage tissue. Further digestion in trypsin or residual digestion in saline for 280 min depleted most of the PG content, as observed in groups A and B. The replacement of trypsin with a physiologic saline solution only slightly slowed the digestion process (group B), while trypsin inhibitors in FBS stopped the digestion in approximately 1.5 h (group C). The normalized digestion fractions of the digested tissues were calculated from ultrasound data and histology sections, and then compared between the groups. Without the use of FBS, 80% to 100% of the full thickness was digested, while this number was only approximately 50% when using FBS. Our findings indicate that the UBM imaging system could provide two-dimensional (2-D) visual information for monitoring progressive trypsin-induced PG depletion in articular cartilage. The system also potentially offers a useful tool for preparing cartilage degeneration models with precisely controlled PG depletion. (E-mail: ypzheng@ieee.org)     

Quantitative Evaluation of Spontaneously and Surgically Repaired Rabbit Articular Cartilage Using Intra-Articular Ultrasound Method in situ

During the last decade, a major effort has been devoted to developing surgical methods for repairing localized articular cartilage lesions. Despite some promising results no ultimate breakthrough in surgical cartilage repair has been achieved. Improvements in repair techniques would benefit from more sensitive and quantitative methods for long-term follow-up of cartilage healing. In this study, the potential of a new ultrasound technique for detecting the compositional and structural changes in articular cartilage after surgery, using recombinant human type II collagen gel and spontaneous repair was, investigated. Rabbit knee joints containing intact (n = 13) and surgically (n = 8) or spontaneously (n = 5) repaired tissue were imaged in situ at 6 months after the operation using a clinical intravascular high-frequency (40 MHz) ultrasound device. Based on the ultrasound raw data, ultrasound reflection coefficient (R), integrated ultrasound reflection coefficient (IRC), apparent integrated backscattering coefficient (AIB) and ultrasound roughness index (URI) were determined for each sample. URI was significantly higher in both repair groups than in intact cartilage (p < 0.05). The reflection parameters (R and IRC) were significantly lower in surgically repaired cartilage (p < 0.05) than in intact cartilage. Furthermore, AIB was significantly higher in surgically repaired cartilage than in intact tissue (p < 0.05). To conclude, the integrity of the rabbit articular cartilage repair could be quantitatively evaluated with the nondestructive ultrasound approach. In addition, clinically valuable qualitative information on the changes in cartilage integration, structure and composition could be extracted from the ultrasound images. In the present study, the structure and properties of repaired tissue were inferior to native tissue at 6 months after the operation. The applied ultrasound device and probes are FDA approved and, thus, applicable for the quantitative in vivo evaluation of human articular cartilage. (E-mail: tviren@hytti.uku.fi)     

An Ultrasound Biomicroscopic and Water Jet Ultrasound Indentation Method for Detecting the Degenerative Changes of Articular Cartilage in a Rabbit Model of Progressive Osteoarthritis

It is important to assess the early degeneration of articular cartilage associated with osteoarthritis (OA) for early intervention and treatment planning. Previously, we have developed a high frequency ultrasound and water jet indentation method for the morphologic, acoustic and mechanical assessment of articular cartilage, using the enzymatic digestion as a model of osteoarthritic degeneration. No naturally degenerated articular cartilage has been tested with the developed method. In this study, we aimed to determine the usefulness of the developed method for detecting the natural degeneration of articular cartilage in a standard surgical model of OA in rabbits. Forty adult New Zealand white female rabbits were used in this study, which included 30 experimental rabbits undergoing the right anterior cruciate ligament transection surgery and 10 control rabbits. At the 3^rd, 6^th, and 9^th week post-surgery, 10 experimental rabbits were sacrificed, respectively, for assessment of the knee cartilage quality. The cartilage at the medial and lateral femoral condyles and tibial plateaus (four points) was measured by the high frequency ultrasound biomicroscopy, the water jet ultrasound indentation and a contact mechanical indentation test before a histopathologic analysis for grading of degeneration severity. Measured parameters were compared among different groups classified either by post-surgery time or by histopathologic grade. The results showed a general trend of increase for ultrasound roughness index and a general trend of decrease for integrated reflection coefficient, stiffness coefficient from water-jet indentation and Young's modulus (E) from the mechanical indentation with the increase of post-surgery time. Comparisons among groups with different histopathologic grades showed similar trend with the increase of degeneration severity. The water jet ultrasound indentation method was demonstrated to be an effective method to measure the mechanical properties of the articular cartilage and with further development of arthroscopic ultrasound probe; it has the ability to assess the early degeneration of articular cartilage with measurement of morphologic, acoustic and mechanical properties of the cartilage in vivo.     

Electromechanical Wave Imaging of Biologically and Electrically Paced Canine Hearts in Vivo

Electromechanical Wave Imaging (EWI) has been show capable of directly and entirely non-invasively mapping the trans mural electromechanical activation in all four cardiac chambers in vivo. In this study, we assessed EWI repeatability and reproducibility, as well as its capability of localizing electronic and, for the first time, biological pacing locations in closed-chest, conscious canines. Electromechanical activation was obtained in six conscious animals during normal sinus rhythm (NSR) and idioventricular rhythms occurring in dogs with complete heart block instrumented with electronic and biologic pacemakers (EPM and BPM respectively). After atrioventricular node ablation, dogs were implanted with an EPM in the right ventricular (RV) endocardial apex (n = 4) and two additionally received a BPM at the left ventricular (LV) epicardial base (n = 2). EWI was performed trans thoracically during NSR, BPM and EPM pacing, in conscious dogs, using an unfocused transmit sequence at 2000 frames/s. During NSR, the EW originated at the right atrium (RA), propagated to the left atrium (LA) and emerged from multiple sources in both ventricles. During EPM, the EW originated at the RV apex and propagated throughout both ventricles. During BPM, the EW originated from the LV basal lateral wall and subsequently propagated throughout the ventricles. EWI differentiated BPM from EPM and NSR and identified the distinct pacing origins. Isochrone comparison indicated that EWI was repeatable and reliable. These findings thus indicate the potential for EWI to serve as a simple, non-invasive and direct imaging technology for mapping and characterizing arrhythmias as well as the treatments thereof.     

Ultrasound Backscatter Imaging Provides Frequency-Dependent Information on Structure,Composition and Mechanical Properties of Human Trabecular Bone

The strength as well as the acoustic properties of trabecular bone are determined by its structure and composition. Consequently, tissue structure and compositional properties also affect the ultrasound propagation in bone. The diagnostic potential of ultrasound has not been fully exploited in clinical quantitative ultrasound devices. The aim of this study was to investigate the ability of quantitative ultrasound pulse-echo imaging, conducted over a broad range of frequencies (1 to 5 MHz), to predict the mechanics, composition and microstructure of trabecular bone. Ultrasound reflection and backscatter parameters correlated significantly with the ultimate strength of the trabecular bone and the bone volume fraction (r = 0.76–0.90, n = 20, p < 0.01). Ultrasound backscatter associated significantly (independently of bone structure or mineral content) with the collagen content of the bone matrix (r = 0.75, r_adjusted = 0.66, p < 0.01). Interestingly, the applied ultrasound frequency seemed to relate the sensitivity of ultrasound backscatter to different properties of trabecular bone. At frequencies ranging from 1 to 3.5 MHz, the ultrasound backscatter associated significantly with the tissue mechanical and structural parameters. At 5 MHz, the composition of the bone matrix was a more significant determinant of the measured backscatter. This study provides useful information for optimizing the use of pulse-echo measurements, and thereby further emphasizes the diagnostic potential of the ultrasound backscatter measurements of trabecular bone.     

Characterization of center frequency and bandwidth of broadband ultrasound reflected by the articular cartilage to subchondral bone interface

Osteoarthritis (OA) produces degenerative changes both in articular cartilage and subchondral bone. During OA, reflection of high frequency ultrasound from the cartilage-bone interface is affected by both changes in attenuation of the cartilage layer and acoustic properties of the interface. The objective of this study was to experimentally investigate the spectral content of ultrasound reflection from the cartilage-bone interface. Specifically, we analyzed the center frequency and -6 dB bandwidth of the broadband high-frequency (40 MHz) ultrasound signal. Intact bovine articular cartilage samples with and without the underlying subchondral bone (n = 6) were measured in vitro using a commercial high-frequency ultrasound scanner. Furthermore, the diagnostic potential of the measurement of center frequency and bandwidth for OA was studied with another series of bovine articular cartilage samples (n = 40) after enzymatic degradations of tissue proteoglycans and collagen. Compared with the reference spectrum at the same depth from a perfect reflector, a major downshift (>51%) of the center frequency and a reduction (>42%) of the bandwidth were observed in both sample groups when analyzing the ultrasound reflection from the cartilage-bone interface. The results suggest that attenuation in the cartilage layer primarily controls the observed downshift of the center frequency and acoustic properties of the subchondral bone play only a minor role in affecting the spectrum of the cartilage-bone interface. Changes in the ultrasound bandwidth of the cartilage-bone interface signals, compared with reference signals, were found to vary more than those in the center frequency in both cartilage sample groups. Compared with pretreatment values, a significant downshift in center frequency (p < 0.01) and a minor reduction in bandwidth of spectra from the cartilage-bone interface were recorded after chemical degradation of proteoglycans with trypsin. In contrast, center frequency and bandwidth of the echoes from the cartilage-bone interface did not change after the chemical degradation of cartilage collagen fibrils. The results suggest that proteoglycan loss, typical to OA, may be detected via the changes in the center frequency of the ultrasound reflected from the cartilage-bone interface. (E-mail: ypzheng@ieee.org, simo.saarakkala@oulu.fi)     

Effects of Vascularity and Differentiation of Hepatocellular Carcinoma on Tumor and Liver Stiffness: In Vivo and in Vitro Studies

Tissue stiffness has been found to be a useful predictor of malignancy in various cancers. However, data on the stiffness of hepatocellular carcinomas (HCCs) and their background livers are contradictory. The aim of this study was to investigate the effects of vascularity and histologic differentiation on HCC stiffness. Elastography point quantification (ElastPQ), a new shear wave-based elastography method, was used to measure liver stiffness in vivo in 99 patients with pathology-proven HCC. Lesion vascularity was assessed using contrast-enhanced ultrasound, computed tomography and/or magnetic resonance imaging. The association of HCC vascularity and differentiation with liver stiffness was determined. In addition, in vitro stiffness of 20 of the 99 surgical HCC specimens was mechanically measured and compared with in vivo measurements. We found that in vivo stiffness was significantly higher than in vitro stiffness in both HCCs and their background livers (p < 0.0001). Moreover, significantly higher stiffness was observed in hyper-vascular and poorly differentiated lesions than in hypo-vascular (p = 0.0352) and moderately to well-differentiated lesions (p = 0.0139). These in vivo and in vitro studies reveal that shear wave-based ultrasound elasticity quantification can effectively measure in vivo liver stiffness.     

Improved Tracking Performance of Lagrangian Block-Matching Methodologies Using Block Expansion in the Time Domain: In Silico, Phantom and in Vivo Evaluations

The aim of this study was to evaluate tracking performance when an extra reference block is added to a basic block-matching method, where the two reference blocks originate from two consecutive ultrasound frames. The use of an extra reference block was evaluated for two putative benefits: (i) an increase in tracking performance while maintaining the size of the reference blocks, evaluated using in silico and phantom cine loops; (ii) a reduction in the size of the reference blocks while maintaining the tracking performance, evaluated using in vivo cine loops of the common carotid artery where the longitudinal movement of the wall was estimated. The results indicated that tracking accuracy improved (mean = 48%, p < 0.005 [in silico]; mean = 43%, p < 0.01 [phantom]), and there was a reduction in size of the reference blocks while maintaining tracking performance (mean = 19%, p < 0.01 [in vivo]). This novel method will facilitate further exploration of the longitudinal movement of the arterial wall.     

Relationships Between Quantitative Pulse-Echo Ultrasound Parameters from the Superficial Zone of the Human Articular Cartilage and Changes in Surface Roughness,Collagen Content or Collagen Orientation Caused by Early Degeneration

We aimed to quantitatively investigate the relationship between amplitude-based pulse-echo ultrasound parameters and early degeneration of the knee articular cartilage. Twenty samples from six human femoral condyles judged as grade 0 or 1 according to International Cartilage Repair Society grading were assessed using a 15-MHz pulsed-ultrasound 3-D scanning system ex vivo. Surface roughness (R_q), average collagen content (A₁) and collagen orientation (A₁₂) in the superficial zone of the cartilage were measured via laser microscopy and Fourier transform infrared imaging spectroscopy. Multiple regression analysis with a linear mixed-effects model (LMM) revealed that a time-domain reflection coefficient at the cartilage surface (R_c) had a significant coefficient of determination with R_q and A₁₂ ($R_{\text{LMMm}}^2=0.79$); however, R_c did not correlate with A₁. Concerning the collagen characteristic in the superficial zone, R_c was found to be a sensitive indicator reflecting collagen disorganization, not collagen content, for the early degeneration samples.